Speed governor



J. NADER SPEED GOVERNOR Oct. 16, 1956- 2 Sheets-Sheet 2 Filed Jan. 9,1952 1211 5 17 ZZTT Joseph Nader E7 7 El 2H5 SPEED GOVERNOR JosephNader, Chicago, Ill., assignor to Motordyne Incorporated, Monrovia,Calif, a corporation of California Application January 9, 1952, SerialNo. 265,699

3 Claims. (Cl. 200-80) The present invention relates to an improvedspeed governor, particularly for electric motors.

One common form of speed governors used for small duty motors isdescribed in the Lee Patent No. 1,767,146. T his governor includes arotatable support member which is arranged to be secured on the shaft ofa motor, and a pair of resiliently mounted contacts which open or closewithin a predetermined range of velocity, the contacts being employed inthe energizing circuit of the motor to control the energization of themotor.

One of the major difficulties with speed governors of the type describedresides in the fact that the operation of these speed governors is veryadversely aifected by changes in temperature and humidity. Evenrelatively small changes in temperature of operation of the motor fromthe temperature at which the switch contact arms were initially set oradjusted can cause a substantial variation in the velocity at which thecentrifugally operated switch elements operate. In general, changes inhumidity also affect the operation of the device in a similar manner. Asa result, changes in temperature and humidity make operation of thistype of speed governor erratic. In installations where the motor is usedas a frequency control device, as in inverters for alternating currentsupplies in aircraft, this erratic operation due to changes intemperature and humidity provides a serious problem,

One of the features of the present invention resides in a structure fora speed governor in which the effects of temperature are compensated forby proper selection of the materials used in the manufacture of therotatable support element and the resiliently mounted switch elements.In a preferred embodiment of the present inven tion, the support memberis made from a material having a low coefficient of thermal expansion,and a modulus of elasticity which decreases with increase intemperature. On the other hand, the switch arms are made from materialswhich also have a low coefficient of thermal expansion, but have theproperty of becoming more rigid rather than more flexible upon anincrease in temperature, or at least do not become less rigid uponincrease in temperature. As a result, as the resilient switch arms areshifted due to the thermal expansion of the support member, theincreased rigidity of the resilient switch arms compensates for thiseffect with the result that the switch operates at a predeterminedvelocity substantially equal to the predetermined velocity desired, eventhough the motor is operated at a higher temperature than that at whichthe setting of the resilient switch arms was originally made.

Another feature of the present invention resides in an improved type ofcommutator construction in the assembly through which the polarity ofthe voltage being supplied to the contact elements is periodicallyreversed, thereby materially increasing the useful life of the contacts.In addition, the commutator structure of the present invention includesspecially designed conducting rings having an increased resistance tothe detrimental effects of relatively high humidity.

nited States Patent An object of the present invention is to provide animproved speed governor assembly for electromagnetic machines which willoperate at a predetermined velocity over a wide range of temperature andhumidity conditions.

Another object of the present invention is to provide an improved speedgovernor for electric motors that is rugged in construction, but simpleand inexpensive to manufacture.

Another object of the present invention is to provide an improvedelectromagnetic machine assembly including the improved governor of thepresent invention.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its manner of construction and method ofoperation, together with further objects and advantages may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings, in which:

Figure 1 is a plan view of a motor equipped with the improved governorassembly of the present invention, with parts thereof broken away toillustrate more clearly the structure;

Figure 2 is a view in elevation, on a magnified scale, of the supportmember and switch assembly of the governor;

Figure 3 is a cross sectional view, with parts in elevation, of theimproved commutator of the present invention;

Figure 4 is an exploded view of the elements making up the commutatorillustrated in Figure 3; and

Figure 5 is a diagram of the eelctrical circuit, of the motor,illustrating the manner in which the switch contacts of the governor aredisposed in the electrical circuit of the motor.

As shown on the drawings:

Referring first to Figures 1 and 2 of the drawing, there is illustratedan electric motor 10 of the D. C. shunt type. It will be recognized, ofcourse, that the invention is equally applicable to other types ofmotors such as series or compound motors. The motor 10 has a shaft 11extending therefrom, what carries a governor assembly 12, a set screw 13being provided to lock the governor 12 in fixed position along the shaft11.

The governor assembly 12 includes a disc-like support 14 and acommutator 15. Structural details of the latter will be described morefully in connection with the description of Figures 3 and 4.

The motor 10 also carries a pair of support brackets 17 and 13 having apair of oppositely disposed brush holders 19 and 20 secured at the endsthereof. The brush holders 19 and 20 carry a pair of conventionalspringpressed brushes 21 and 22 which engage the commutator i5 andserves to reverse periodically the voltage applied to the switch arms ofthe governor.

As best seen in Figure 2, the support 14 includes an integral upstandinghub portion 24 having an internal bore of sufiicient diameter to receivethe shaft 11 of the motor 10 in closely fitting relation. The hub 24receives the commutator 15 in close fitting relation, as willhereinafter be described.

The support 14 is provided with suitable recesses to accommodate theswitch elements of the governor assembly. These switch elements includea pair of resilient switch arms 26 and 27, each carrying a contactbutton 28 and 29, respectively. The fixed ends of the switch arms 26 and27 are secured to an internal wall 30 of the support 14 by means of apair of securing screws 31 and 32.

As shown in Figure 2, the commuator 15 is divided into conductingportions 34 and 35. The conducting portion 34 electrically connected tothe switch arm 27 by means of a conductor 36 and 2. lug 37. An insulatorstrip 38 insulates the strip 37 from the wall 30. A pair of insulatingstrips 39 and 40 separate the switch arm 26 from the switch arm 27. Theconducting portion 35 of the commutator 15 is electrically connected tothe switch arm 26 by the provision of a conductor 42 and a lug 43. Aninsulator strip 44 insulates the switch arm 26, from a strip 45 intowhich the screws 31 and 32 are threaded. It will be appreciated that thescrews 31 and 32 are electrically insulated from the switch contact arms26 and 27, as by means of an insulating bushing about the screws 31 and32.

The spacing between the contact buttons 28 and 29, which determines theangular velocity at which centrifugal force will cause the switch tooperate is determined by means of a screw 48 adjustably threaded into asupport member 49. The end of the screw 43 carries a glass ball St) orother insulating medium in abutting contact with the switch arm 27.

The material of the support 14 is chosen for its low coelficient ofthermal expansion. A suitable material for this purpose is analuminum-silicon alloy, such as one containing 12% silicon and 88%aluminum. However, even with materials having relatively lowcoeflicients of expansion, the expansion of the support 14 as a resultof an increase in temperature causes a shift in the switch arms 26 and27 such that the operating point, i. e., the velocity at which thecontact arms 26 and 27 close, is varied. To compensate for this effect,the switch arms 26 and 27 are made from a material which also has a lowcoefficient of thermal expansion, but has the additional property of notincreasing its flexibility as the temperature increases. Preferably, thematerial for the switch arms 26 and 27 is one which actually becomesless flexible as the temperature increases, that is, a material having amodulus of elasticity which increases with an increase in temperature.

Several types of alloys having these properties are available for theswitch arms. A typical example of one such alloy is a nickel-iron alloycontaining about 42% nickel, 4 /2% chromium, 2 /2% titanium, .06%carbon, .4% manganese, .5% silicon, .4% aluminum and the balancesubstantially all iron. The decreased flexibility at elevatedtemperatures of the metals described above has been found to compensateadequately for the expansion of the support member carrying the switcharms so that a relatively constant operating point can be achieved overa wide range of temperatures. Using a speed governor of the typedescribed in an inverter assembly, I have found that the frequency inthe generated A. C. voltage can be maintained to within an error of 1%over a temperature range from 55 C. to 75 C. This represents asubstantial improvement over the operating characteristics of theconventional centrifugal type speed governors.

Another factor of importance in preventing erratic operation of thespeed governor is the change in humidity which the governor encountersin use. The effects of humidity are especially troublesome in thecommutator of the speed governor. The commutator structure illustratedwith particularity in Figures 3 and 4 of the drawings effectivelyresists the adverse effects of changes in humidity. As best shown in theexploded view of Figure 4, the commutator includes a metallic spool 52having an enlarged head portion 53. The spool has an axial bore 54arranged to be received over the hub 24 of the support 14 in closelyfitting relation. An inverted V- ring 55 of an electrical insulatingmaterial, such as mica, having a high resistance to moisture penetrationis seated against the enlarged head 53 in nested engagement. A sleeve 56of insulating and moisture resistant properties is next placed over thebarrel of the spool 52 and against the inverted V-ring 55. The sleeve 56preferably also composed of mica, forms a base support for theconducting segments making up the commutator structure. This structureconsists of a plurality of individual, circumferentially spacedconducting segments 57 whose inner ends are dovetailed as indicated at58 to be received in the insulator V-rings. Each of the segments 57 ispreferably coated with a highly conductive material such as silver. Theplurality of segments 57 is then arranged in a ring, and a pair of micainsulating strips 59 and 6% (Figure 2) are disposed at diametricallyopposite portions of the conducting ring thus formed to provide the pairof conducting portions 34 and 35. The conducting segments may be pressedtogether with the mica strips interposed in a hydraulic press to cause asuperficial bonding of the individual segments 57 into a composite ring.It will be appreciated that the commutator structure can be divided intomore than two conducting portions, to thereby cause more than one cycleof current reversal during each revolution of the commutator.

The preferred ring is then slipped over the mica sleeve 56, and a secondV-ring 62 is then fitted over the barrel 52 to center the conductingring between the V-rings and 62. Next, a metallic V-ring 63 is placedover the barrel 52. As indicated in Figure 3, an end 64 of the spool 52may be flared outwardly to prevent the \.'-ring 63 from slipping off theend of the spool.

As another alternative, the conducting portions on the commutator can bemade from solid machined bars of arcuate shape, and the body of thecommutator which may be composed of synthetic resins such as Bakelitemay then be molded around the preformed, solid conducting portions.

A circuit in which the speed governor of the present invention isincluded is schematically illustrated in Figure 5. In this drawing, a D.C. shunt motor having an armature 65 is energized by means of a shuntfield winding 68. A current limiting resistor is in series with theshunt field winding 68. The electrical switch con tacts 26 and 27 are inparallel circuit relationship with the resistor 70, and as the motorbuilds up to a predeter mined speed, the centrifugal force on thegovernor closes the contacts 26 and 27, thus shorting out the resistor70. The elimination of the resistor 70 from the circuit causes acorresponding decrease in the speed of the motor. As the motor speeddecreases, the centrifugal force urging the contacts 26 and 27 closedalso decreases, until the centrifugal force is insuflicient to hold theresilient contact arms 26 and 27 closed. At this time, the switch opensand the resistor 70 is again inserted in series with the shunt fieldwinding 68, thereby increasing the angular velocity of the motor.

While the governor of the present invention has been specificallyillustrated used in conjunction with a D. C. shunt motor, it will alsobe evident that the governor will find use in other types of motors andin electromagnetic machines generally where speed control is to beachieved.

The governor of the present invention has several distinct advantagesover similar governors heretofore used. One of the main advantagesarises from the novel correlation of the flexibility of the switchcontact arm with the thermal expansion and increases flexibility of therotatable support member due to increases in temperature. Further, thenovel structure of the commutator of the present invention effectivelyresists the adverse effects of increased humidity. Furthermore, by thearrangement of the commutator segments in the manner indicated, thebrushes which cooperate with the commutator act against the commutatoralong radial lines, rather than imposing an axial thrust against therotating governor as in conventional governor assemblies. Thisstructural feature is advantageous from the stand point of securingproper alignment between the commutator and the contracting brushes.

It will be evident that various modifications and variations may beeffected without departing from the scope of the novel concepts of thepresent invention.

I claim as my invention:

1. A speed governor assembly comprising a rotatable support member, apair of switch arms carried by said support member, said support memberbeing composed of a material which becomes more flexible upon anincrease in temperature, and said switch arms being composed of amaterial which becomes less flexible on increase in temperature.

2. A speed governor assembly comprising a rotatable support member, apair of resilient switch arms carried by said support member, saidsupport member being composed of a material having a relatively lowcoefiicient of thermal expansion and a modulus of elasticity whichdecreases with an increase in temperature, and said switch arms beingcomposed of a material having a relatively low coefiicient of thermalexpansion and a modulus of elasticity which does not decrease withtemperature.

3. In a speed governor assembly including a rotatable support member,and a pair of resilient switch arms carried by said support memberarranged to close upon rotation of said support member at apredetermined angular velocity, a tension adjusting means comprising ascrew carried by said support member in threaded engagement, and acontact member comprising a glass ball carried by one end of said screwand arranged to engage one of said switch arms to vary the spacingbetween said switch arms upon axial movement of said screw.

References Cited in the file of this patent UNITED STATES PATENTS854,781 Underwood May 28, 1907 1,061,251 Burke May 6, 1913 1,415,370Lehman May 9, 1922 1,551,598 Winter Sept. 1, 1925 1,632,565 Schmidt June14, 1927 1,767,146 Lee June 24, 1930 1,855,703 Cloud Apr. 26, 19322,103,589 Lee et al. Dec. 28, 1937 2,444,799 Wood et a1. July 6, 19482,454,067 Kohl Nov. 16, 1948 2,480,590 Merrill Aug. 30, 1949 2,557,208Thunberg et al. June 19, 1951

